Due to threats of global warming, pursuant to Kyoto Protocol and Copenhagen Protocol, various countries start to mitigate carbon emission, and thus carbon emission regulations are gradually strict. In addition to complying with the requirements and schedule of the use of relevant refrigerants, refrigerating and air conditioning industrials also need to practically consider the performance maintenance in the application of new generation of refrigerant/refrigeration oil, the continuation of existing equipments, technical feasibility, safety, and application cost, etc.
The new generation of environmentally friendly refrigerants generally include hydrofluoroolefins (HFO) and the mixture thereof, ammonia (R717), carbon dioxide (R744), hydrocarbons (such as R290, R600, etc.), and difluoromethane (R32) etc. Use of hydrofluoroolefins (HFO) and the mixture thereof needs to consider the application cost, ammonia (R717) has problems of toxicity and corrosion, carbon dioxide (R744) refrigerant involves higher equipment cost, and the hydrocarbon refrigerant has potential problems of inflammability and explosion. However, since ozone depletion potential (ODP) by difluoromethane (R32) belonging to HFC refrigerants is zero and its Global Warming Potential (GWP) is only about ⅓ of HFC refrigerants such as conventional R410A (mixed components) or R134A (single component), it has been widely applied to various mixed refrigerants to balance GWP effect. Thus, based on the consideration of the comprehensive properties, R32 refrigerant is considered as one of a next generation of environmentally friendly refrigerants which have most applicability
Difluoromethane (R32) refrigerant has been produced and applied from 1990s in a large scale. The existing mixed refrigerants, such as R410A, R407C etc., are the mixtures of difluoromethane (R32). R32 refrigerant is one of the lowest cost and most widely used refrigerants. However, because of its immiscibility with the refrigeration oil suitable for the existing HFC refrigerants, it is not widely used individually until now. Therefore, under the circumstance of lacking the combination with suitable refrigeration oil, difluoromethane can only be mixed with other HFC refrigerants having high GWP (greenhouse effect index) to meet the conditions of existing applications. For example, the components of the common R410A refrigerant is R32/R125 (50/50), whose GWP is up to 1725, and that of R32 itself is only 650. If R410A refrigerant is completely replaced with R32, GWP will be reduced up to 62%.
Although samely classified to HFC refrigerants, difluoromethane (R32) is not applicable environmentally friendly refrigeration oils which are exclusively for a serial of commercially available HFCs developed as of 1990s are not suitable for difluoromethane (R32). The refrigeration oils suitable for use with difluoromethane (R32), which are disclosed in TW 201333177 A1 (Patent Reference 1) or TW 201435080 A1 (Patent Reference 2) or under development, focus to solve the problems of miscibility, which is mainly implemented by using specific branched chain fatty acids to increase miscibility. The cost of the specific branched chain fatty acids, such as 2-methylbutanoic acid, 2-methylpentanoic acid, 2-ethylbutanoic acid (Patent Reference 1) and 2-methylpropanoic acid (Patent Reference 2) etc., is relatively high, and the difference of the miscibility with R32 refrigerant of the specific branched chain fatty acids in combination with the fatty acids such as 2-ethylhexanoic acid or 3,5,5-trimethylhexanoic acid, is so large that stable miscibility cannot be controlled easily. When a compressor requires the refrigeration oil to be different viscosity or miscibility for application, it is difficult for the structure claimed in TW 201333177 A1 to get a solution in a program involving complete miscibility for the kinematic viscosity of 22 to cSt (40° C.) due to the limitation of the structure. The POE having fully branched chain structure mentioned in TW 201333177 A1 causes a low Viscosity Index (usually equal to or less than 95). Due to the fact that the viscosity decreases significantly as the running temperature increases, after combining with refrigerant, this type of refrigeration oil tends to cause insufficient lubricity and causes the equipment worn out or showing a low running performance. This type of refrigeration oil needs to combine with a specific additive to ensure the normal running of refrigeration system due to the consideration of lubricity and wear. The use of a specific additive is not beneficial to commercial extension and results in increasing the application cost.
Reference 2 (Takeshi Okido, Katsuya Takigawa, Hitoshi Takahashi, “Development of Refrigeration Oil for Use With R32”, 15th International Refrigeration and Air Conditioning Conference at Purdue, Jul. 14-17, 2014) and TW 201435080 A1 (Patent Reference 2) adopts a complex ester to improve the application property by adjusting the viscosity index and miscibility of the disclosed refrigeration oil. Since the different polymerization of the complex ester will significantly affects viscosity and miscibility of the refrigeration oil, and the ester structures of the non-neopentyl polyol of the complex ester are unfavorable to hydrolysis stability and high temperature stability, there is a need to especially consider the combination of the complex ester with additives or the increase on the does thereof. Moreover, the miscibility of the complex ester sharply vary with viscosity, and thus are not suitable for the refrigeration oil having low viscosity of less than ISO VG 46 (included) or high viscosity of more than ISO VG 120 (included).
There are other manufacturers who adopt super strong acids or solid acids to simultaneously conduct different degrees of condensation and esterification of organic acid to obtain POE having various viscosity and miscibility, and the POE is mixed. However, since it is difficult to control the degree of polymerization, viscosity and miscibility vastly vary and the production is not carried out in large scale commercially. Moreover, the polymerization reaction involves using super strong acids, thereby resulting in low yields and unfavorable cost control.